1. Field of the Invention
The present invention relates to a control system, and particularly to a variable wattage control system. More specifically, the present invention relates to a variable wattage control system for a power-receiving device, such as the heating element.
2. Prior Art
Control systems for controlling the power output applied to a heating element or other power-receiving device are well known in the art. In particular, U.S. Pat. No. 3,752,956 to Cahill et al.; U.S. Pat. No. 4,582,982 to Peigari; U.S. Pat. No. 4,894,520 to Moran; and U.S. Pat. No. 5,624,591 to Di Trapani all disclose some type of controller for controlling the power output to a heating element. Specifically, the Peigari reference teaches an SCR power controller in which the output voltage to a resistance heater is varied in accordance with outside temperature, while the Moran reference applies a variable current to a resistance heater corresponding to variations in supply voltage by using a pulse width modulator which controls the timing of a switching device in order to control the flow of current through the resistance heater. Additionally, the Cahill et al. reference discloses a fixing circuit in arrangement with a gated triac and feeding circuits for controlling power output to a heating element. Finally, the Di Trapani reference teaches a control circuit comprising a triac for modulating the current supply to a heating element such that the flow of current is interrupted thereto when a predetermined threshold is reached.
However, further enhancements in power control systems are desirable. More specifically, there is a need in the art for a power controller that can convert at least one power-receiving device, such as a heating element, having a single wattage rating to a heating element having multiple wattage applications. There is a further need in the art for a controller that has the ability to limit the maximum wattage to a value less than that which would be provided at full line voltage, and which provides a scaling function for re-scaling the power output to the heating element in order to better control the power output. Further, there appears a need for a controller that permits manual input of various parameters for determining the desired scaling function by the user. Further, there appears a need for a method of enhancing phase angle power control at low conduction angles.